This invention generally relates to circuit breakers with tripping circuits and it specifically relates to circuit breakers with ground fault trip control circuits.
U.S. Pat. No. 3,818,275, issued June 18, 1974, to A. B. Shimp and assigned to the assignee of the present invention discloses a circuit interrupter system for sensing fault current in a line to be protected, for deriving intelligence about the status of the fault current and for causing the circuit interrupter to initiate a tripping action when the fault current reaches a predetermined level. After the tripping action has been initiated sufficient energy for continuing the tripping operation to its completion is derived from the fault current. Consequently the control system provides intelligence concerning the proper time to trip the circuit breaker prior to the actual tripping operation but does not provide any tripping energy as it is obviously not needed at this time. After the tripping operation has begun, the control system provides tripping energy and no intelligence, as obviously intelligence is no longer needed. However, it is sometimes desirous to sense the presence of ground fault current in a line to be protected and to cause a tripping operation based on the presence of the ground fault current. Since ground fault current may not be of sufficient magnitude to supply tripping energy during that part of the tripping operation when it is needed, it would be advantageous if a separate energy deriving circuit utilizing only ground fault current could be provided for substantially guaranteeing the completion of the ground fault tripping operation once it has begun.